Process for forming a sheet-metal sheel for a spark-plug.



AV ILABLE COPY w. E. SHERBONDY. PROCESS FOR FORMING A SHEET METAL SHELL FOR A SPARK PLUG.

APPLICATION FILED AUGJ. I914. 1,152,983. Patentedsept 7,1915.

2 SHEETS-SHEET I.

4 a 'INVENTOR.

Patented Sept. 7

2 SHEETS-SHEET 2.

W. E. SHERBONDY.

PROCESS FOR FORMING A SHEET METAL SHELL FOR'A SPARK PLUG. 1,152,983.

APPLICATION HLE D AUG-7. i914.

WITNESSES:

W A TTORNE YX masses.

UMTEE @TATES na r- WILLIAM E. SHEBBONDY, 0F CLEVELAND, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS,

CURPORATION 0)? 01-110.

TO THE BIGSBY ROTARY MANUFACTURING COMPANY. OF CLEVELAND, OHIG, A.

PB-GGESS FOR FORMING A SHEET-METAL SHELL FOR A SPARK-PLUG.

Specification of Letters Yatent.

Patented Sept. 2', 1915.

Application filed August 7, 1914. Serial No. 855,601.

T 0 all whom it may concern: 7

Be it known that 1, WILLIAM E. SHER- BQNDY, a citizen of the United States, and resident of Cleveland, in the county of Cuyahoga and State of Ohio, have iny entcd certain new and. useful Improvements in Process for Forming a Sheet-Metal Shell for a. Spark-Plug, of which I hereby declare the following to be a full, clear, and exact description, such as will enable others skilled in 'the art to which it appertains to make and use the same.

The objects of the invention are to provide a mechanical process comprising step by step operations whereby the shell of a metal spark plug can be constructed from sheet metal, and provided with an opening for the accommodation of the electrode.

At the present time a large expense has to be incurred in the installment of automatically acting machinery to construct the spark plugs from bar metal stock, which necessitates a large amount of waste in scrapped material, and although in every way an ineilicieut and expensive method of producing theplugs it has hitherto been an unavoidable one, since no other method has been known. I

By means of the present improved process the shells can be piarduced from sheet metal by means of drawing and forming dies and parts which have hitherto been difficult of shaping on account of the hexagonal sides and angles find inner and outer shoulders can be manufactured at ti-l'l'llicll greater rate of speed and with comparatively littl loss of material in the form of scrap.

The amount of labor involved in producing the shells and the accompanying expense is also very greatly reduced. Further, the initial expense of the sheet metal employed in'the manufacture of shells for spark plugs is reduced-from to below the expense of manufacturing the shells from bar stock, and substantially also without any waste of material in forming the body of the plug, after the blank has been cut.

Further,important features comprise the to be formed.

To accomplish the desired results particular attention has been paid to the features required in the several dies to obtain the greatest efficiency in each step of the process without which it would be impossible to carry out the various succeeding steps.

The several steps of the process and the manner of obtaining the gradual changes in the shape of the sheet metal to produce the finished article are illustrated in the accompanying drawings, hereinafter described, and clearly pointed out in the claims;

1 In the accompanying drawings Figure l is a vertical central section showing the sheet metal blank from which the body of the shell of a spark plug is formed and the dies for cutting out the same; Fig. 2 is a similar section showing the blank formed into the shape of a cup and the forming dies therefor, and alsoa stripping device; Fig. 3 is a similar section showing'the method of further elongating the cup, reducing the diameter of the lower portion thereof while retaining the diameter and somewhat upsettingthe upper portion of the shell; Fi 4 is a section similar toFig; 3, showing tie same function carried further and the lower portion of the cup still further reduced in diameter, and elongated, preparatory to forming the hexagonal faces upon the upper portion of the cup; Fig. 5 is a similar section showing the same 'functions for the dies that are shown in Figs. 3.and 4, and forming the body of the shell ready for the hexagonal shape of theupper portion; Fig. 6 is a similar section showing 7 is a plan view of the die; Fig. 8 is a sectional view showing a continuation of the process of reducing the hexagonal portion in diameter and elongating it; Fig. 9 is a completion of the shell from a sheet metal plan view thereof; Fig. 10 is a similar view blank into the conformation desired with showing. the hexagonal portion still further the fewest number of operations compatible reduced and elongated; Fig. 11 is a plan with the perfect shaping thereof. view thereof; Fig. 12 is a. similar section showing the final formation, including upsetting the body portion and giving the precise finished shape and size to every part; Fig. 13 is a similar view showing the cutting away of the end of the shell of the spark plug to provide an opening through which the inner electrode may proring seated upon shoulders at the angles takes the place of the projecting shoulderto make the plug gas tight. The shell having tapered sides does not require this shoul der since it closes the opening completely. fBoth shells are provided with hexagonal 4 sides at their upper extremities andboth' can be made by-this process.

As stated very heavy materlal is required in the construction of the spark plugs for 3 the purposes of first obtaining the exterior shape and for cutting the screw thread therein and secondly to enable theinternal shoulder to be formed, which is theseat of the inner insulation orcore', and to cut a screw thread if desired Within the body wall to retain the bushing or sleeve nuttha-t ordinarily secures the insulation in place.

In order to produce a hollow body or shell having an exterior portion shaped in the form of an accurate hexagon of given diinensions it is absolutely necessary to make the cup shown, in Fig. 2-of adefinite iixed outside diametento give adefinite diameter .across the fl'atportions of the hexthroughout all the operations, up to'the forming of the angles, and if it is not retained it is impossible'to get a perfect hexagon. 1

Many other features ar found to be of the greatest importance. For instance it has,

beeii found that the disk shaped blank must accurately fit the recess madefor it in the die or the top edge of the cup will be very uneven and after a few operations of the dies the amount of unevenness would multiplv to such an extent that the piece could not be used. m The exact diameter of the first blank requires careful experiment and calculation and is not an obvious thing to the best skilled mechanics, since many features which are learned only by experiment control the subsequent shaping the metal.

- Theradius marked ain Fig. 2 must be .and form an imperfect end. ever this radius is exactly rlght and the dies agonal part, the shoulder and the inner j The various shell of the spark plug is completed and the of an exact predetermined length or when the blank is formed the metal will stretch \Vhen howare of the right size the tendency of the metal is to thicken on .the upper portion of the cup, which is of a very important feature, so as to provide substance sutiicient to fill out the angles of the hexagon later on. in the process, but which must be gradually provided for during the process.

Many experimental forms of dies ineffectually employed to produce the hexagonal body, and the cups have been formedof various sizes and the lower portions have been reduced and elongated and the cup has been then drawn through a hexagonal die, but after carrying out the remaining steps of the process the hexagonal portion has not 1 been properly filled out, nor has the proper 8 thickness of material been retained for the sea-t of the insulation or for the" inside screw thread which receives the screw threaded clamping sleeve. Afterwarda split die of hexagonal shape was attempted, the two halves of which were driven togetheig'and produced a clamping effect upon a large portion of the shell, but after many attempts had been made to employ this die it was given up as e ually impractical as the previous trials. fterward a cup having a reduced lower portion was driven through a die having hexagonal sides, the male die or punch fitting the lower portion of the shell and the upper portion hexagonal, and made to exactly fit the hexagonal die,'but the results were unsatisfactory. Finally a punch and die were formed as shown in Fig. 3 with better results but not yet perfect. It was found that only by making a combination punch having a sleeve thereon. 'the lower portionoi' which engages the upper portion of the shell so as to retain the shellv t when the lower portion of the cup is being agon, and this diameter must be retained reduced in diameter and elongated, the upper portion will be retained of the proper size and will be somewhat upset, which will produce the required thickness for the hex thread.

steps of the process until the various tools employed and the peculiarities of their construction may be described asfollows: In Fig. 1 a sheet of metal M is placed upona female die. A and a male die 13 of the same diameter is employed tostrike out the disk shapedblank C from which the shell 'of the spark plug is formed.

In Fig. 2 the next step of the process is illustrated where the disk C is shown resting in a recess C, of precisely the same diameter as the diskso as to accurately center it and which is formed in a block (3 The block C? is provided with the cylindrical opening fix the shoulder C which is expanded at A at the upper end so as to enter the recess G in a smooth gradual curve. The blank 15 forced through this opening by means of a punch-D having a rounded lower end which forms the cup. The important feature of this step of the process is found in the action of thercunded corners A. of this die, the radius of which is such. as to permit the sides of the cup to be elongated without cracking, which would be the result if the shoulder were abrupt.

in Fig. 3 the next step of the process is shown. Here E is. a punch which has a reduced diameter E which enters the cup as it lies over the cylindrical opening F in the die block F. This opening is of less diameter than the cup- The upper corners of this opening are rounded at F to permit drawing the cup to a reduced size and forming F thereon. As soon as the punch enters. the cup and commences drawing the same down into the die, a sleeve G comes into play. and forces the cup downward, in unison with the drawing movement of the punch, until the lower extremity of the shell. has been suliiciently elongated. The

sleeve G will then compress the upper edge of the shell until it is slightly upset and at the same time the precise internal diameter of the upper end of the cup is retained by the main body of the punch F. A shoulder F on the punch between the portions of different diameter forms the shoulder upon the inner surface of the shelh and an annularrib G upon the lower extremity of the sleeve controls the external diameter thereof.

In Fig. l forming dies of similar shape are employed but the lower extremity of the punch and die are reduced in diameter to still further elongate the .cup ,and reduce the diameter of the lower end, so to be nearly ready for the screw threading of the outer side of the shell. The shoulder formed upon the shell made with a curve of increased radius the lower portion is reduced in size, the utility of which is hereafter explained.

has been found necessary that the punch and die shall be in absolute alinement with each. other, so that the punch willbe per fectly concentric with the die when it enters it, otherwisc the upper and lower portions of.

the shell would not be in perfect alinement, or concentric with each other, and any eccentricity should occur when the hexagonal portion is formed, it would have one side much longer than another, after the shell has been put through the subsequent operations of the process. To produce a perfect hexagon a special gage has been made for alining these tools. The exactmnount of upsetting of the upper and must also be care fully calculated to obtain the precise amount of material required to fill out the angles of y the hexagon upon amend. lf-nccessary a a described are thus formed it is usually necessary to anneal the cup to remove its hardness before the final operatlons of producing the hexagon upon the upper half thereof is carried out.

In El g. 5 the radius from which the shoulder is formed upon the shell is still greater in length to obtain a larger curve therein, and is obtained by the reduction in size of the lower end of the cup while the size of the upper end of the cup remains unchanged.

The method of forming the hexagon is illustrated in'Figs. G, 7 and 8 respectively.

In Fig. 6 a punch H is formed of two diameters to correspond more closely to the finished diameters of the shell, the upper portion being of less diameter thanthe internal diameter oftheuppcr portion of the shell as it leaves the dies shown in Fig. 5, but is largerthan the finished diameter of the inside of the upper part of the shell. I is the female die which forms the exterior of the hexagon. It will be seen that the opening in this die is approximately hcxagonal in shape but the corners are extended outwardly or radially at I and the upper edges of the sides and corners are curved outwardly at I? to permit the metal to flow gradually into the corners so as to fill out the hexagonal shape. p

All the dies shown in Figs. 6, T, and 8 are provided with rounded corners at l but the radial extensions of these corners are gradually reduccd until only sharp hexagonal corners remain, and in'the last used die the final shape is produced. As many intermediate dics may be used as are necessary to draw down the sides into a hexagonal form.

It has been found im 'n'acticable to produce hexagonal sides and perfectly sharp angles upon a cylindrical shellby means of dies of perfect hexagonal shape and having perfect angles, for the reason that a prohibitive number of operations would be required, hence the modifications heretofore described have been made. I

The curves provided the upper edges at J J must be carefully considered in order to enable the larger portion of the shell to enter the die as easily aspossible, and this curve should be a compound curve or cycloidal in shape, and extended low into the die; in a graceful curve, otherwise the reduced extremity of the punch will force a hole in the bottom of the cup before the larger portion of the shell can be drawn down through.the die, expressed outward to fill the angles of the hexagon'g-Also the shoulder upon the shell should notbe too abrupt. or the effectfwouldbe the same, to cause the punch to force out the. bottom ofthe shell before the resistance of the thickened and enlarged portion of the shell has been overcome. I

As shown in Fig. 6 the upper portion of the shell is of less diameter than the extreme diameter of the lip of thedie at J, and

' hence the shell will partially enter the die result.

before the drawing action commences and will be easily started down the curved edges of the die and centered therein. The gen tle slope of the die and the largecurvature of the shoulder on the shell coact to over-' come the great resistance of the large portion of the shell to the drawing action of the punch. The fact that the shell is wholly within the curved portion of the die when Y to form a gas tight joint when a straight parallel sided shell is used. A slight taper at W insures a tight joint. The angles in this case are turned away to make a sharp corner against which the ring fits closely.

Having described the invention what I claim as new and desireto secure by Letters Patent is:

1. An improved method of producing a sheet metal shell for a spark plug, consisting -dies, third, further reducing the-lower por-,

in first cutting a disk of predetermined size from sheet metal from which all the integral parts are to be formed, second, drawing the disk laterally into a cupped form, While rea taining it accurately in absolutely concentric tion while retaining the diameter of the upper portion substantially constant, said diameterof the upper portion being proportionately greater than the outer dimensions of the finished hexagon, next still further reducing the diameter of'the lower portion while retaining the diameter of the upper portion substantially unchanged, next draw ing the cup shaped blank having the reduced andfelongated lower extremity through a forming die forthe upper extremity, and

thereby forming hexagonal sides, and radially and outwardly extending cor'ners thereon, gradually reducing and elongating the sides and reducing the corners, and finally compressing and upsetting the upper portion until the perfect shape is attained.

2. The improved method of constructing sheet metal, consisting in first, cutting a cirupper portion constant and finally forcing the-shell through a die having a hexagonal opening of less diameter than the diameter of the upper portion of said shell, to form the hexagonal sides thereon.

3. An'improved method of producing the shell of a'spark plug from sheet metal having an opening in the lower end to receive the electrode, said shell having a hexagonal upper portion and a reduced lower portion consisting in first cutting a blank disk of predetermined diameter, drawing the same internally into cup form of greater diameter than the greater diameter of the finished cup to elongate it and reduce it in diameter while retaining the diameter of the upper portion unchanged and portion, repeating this operation'until the lower portion is of the prescribed diameter and thickness, reducing thediameter of the upper portion of the cup and simultaneously forming hexagonal sides thereon, and finally cutting away a portion of the lower extrem ity of the cup to form an opening therethrough. p

4. An improved process for constructing a shell for a spark-plug from sheet metal, having-an opening in the lower end to allow for electrode, consisting in, first cutting a shell, then drawing out the lower end of the simultaneously slightly thickening the wall of the upper blank in theform of a. fiat disk from sheet metal, supporting the same in a closely litting die, and drawing the disk laterally by means of an accurately concentric punch to form a cup having its upper edges in a common horizontal plane gradually dra wing out the lower portion to reduce its diameter and elongate tl gsame, and simultaneously form ing a shoulder thereon, and retaining the diameter of the upper portion substantially unchanged, and slightly upsetting'the upper portion tothicken the metal therein, continuing th s part of, the operation until the 1 lower part is substantially of the required diameter,.=' then annealing the shell, and afterward forcing it through a hexagonal die of less diameter than the larger diameter ofthe cup 5.An 1mproved process for constructing a shell for a spark plug, having an opening a spark plug having a hexagonal upper portion and a. reduced lower extremity frompredetermined-size from sheet metal, drawing out the 'disk laterally -to form a cup, drawing out the lower portion of the cup to elongate it and reduce it in size, and 1nean-- while retaining the upper portion of the cup in a fixed position, and slightlv upsetting the same to provide for the increased amount of metal required in filling out the corners of the hexagon, further reducing the diameter of the lower portion and elongating the same until the approximate shape ofthe lower portion has been secured, and

meanwhile rigidly holding the upper portion and slightly upsetting the same, annealing the cup, drawing the cup through a hexagonal dieof less diameter than the cup,

and of approximately the finished size of the shell, to form sides upon the upper portion of the cup and to elongate the same,

giving a final pressure to the cup in dies of finished sizes, and removing a portion of the lower end of the cup to form an opening for the passage of the electrode.

6. An improved method of forming a shell for a spark plug from sheet metal, having an opening in the lower end to allow for electrode, consisting in first forming a cup from a sheet metal blank, reducing the diameter of the lower end thereof and elongating the same, the diameter of the upper portion remaining unchanged and larger than the diameter of the finished hexagon, slightly thickening the upper portion drawing out the upper end of the cup to form hexagonal sides thereon and radially extended angles and continuing the proceedure loy' redrawing the cup to gradually reduce and elongate the hexagonal portion, andreduce the PI'OJGCtlOIlS. at the angles until the required shape and size has been approxi-.

vmately attained, and finally compressing the shell withinclosed dies, to further elongate the lower portion, and accurately form the upper portion to give final shape desired.

7. The method of forming a cup shaped form having a reduced and elongated lower extremity from which form a shell for a spark plug can be made, consisting in first cutting a disk of predetermined diameter from sheet metal, drawing the same into cupped form, and retaining the edges in a common plane, supporting the cup upon a die of less diameter than the cup and having rounded edges, drawing the lower portion while retaining the diameter of the upper tion to rest upon, and in the inner face of which the screw thread can be cut.

In testimony whereof, I hereunto set my hand this 24th day of July 1914c, Y

WILLIAM E. SHERBONDY. In presence of- RALPH W. JEREMIAH, WM. M. Monroe. 

